Conventionally, vibrating wave motors generate a progressive vibrating wave on the drive surface of an elastic body by utilizing expansion and contraction of a piezoelectric body, and elliptic motion is induced on the drive surface by the progressive vibrating wave. A moving element is press-contacting the drive surface of the elastic body, and the moving element is friction driven by the elliptic motion.
On the other hand, a vibrating wave motor using vibrations other than progressive vibrating waves is also known (for example, Patent Document 1). In this type of vibrating wave motor, a cylindrically shaped vibrating element is made to undergo flexing vibrations, and the moving element press-contacting the end surfaces of the vibrating element is friction driven by the flexing vibrations.
Recently, there has been a trend to miniaturize vibrating wave motors and make them lighter by reducing their diameter to approximately one third to one fifth of that of conventional ones. In this miniaturization, a diameter of conventional vibrating wave motors using progressive vibrating waves becomes small and an absolute value of vibrating amplitude becomes small, hence the output performance might be lowered.
The vibrating wave motors generally use, as a vibration source, an electromechanical conversion element such as a piezoelectric element. The piezoelectric element induces a displacement due to expansion and contraction by voltage application, and the displacement per 1V voltage is extremely small, on the order of about several nm. In order to obtain a displacement capable of driving the moving element, a drive signal needs to have a voltage of at least about 80 to 100 Vp-p, and the voltage tends to become high.
Particularly in a vibrating element having the shape as described in the above Patent Document, the electrodes to which the voltage is applied are apart from each other, and the electrostatic capacity is small, thus requiring a higher voltage.
In general, vibrating wave motors use drive signals in a nonaudible vibrating wave range (not less than 20 kHz). Therefore, in order to raise the voltages of the driving signals in the vibrating wave range to a degree that the piezoelectric element can be vibrated, the circuit size might become large and the manufacturing cost might increase.
Patent Document 1: Japanese Examined Patent Publication No. H7-2229.